The present invention relates to a method of forming a bottom oxide layer and conductive layers in a trench, and more particularly to a method of forming a bottom oxide layer and conductive layers in a trench structure of a trench-type power Double-Diffused Metal-Oxide Semiconductor (DMOS) device without formation of voids.
Nowadays, Double-Diffused Metal-Oxide Semiconductor (DMOS) devices are widely used in the semiconductor industry. FIGS. 1(a) to 1(f) are schematic cross-sectional views illustrating a conventional process for forming a bottom oxide layer in a trench structure of a Double-Diffused Metal-Oxide Semiconductor (DMOS) device. As shown in FIG. 1(a), before the manufacture of DMOS devices, a semiconductor substrate 101 is provided first. Then, a pad oxide layer 102, a silicon nitride layer 103 and a first oxide layer 104 are sequentially formed on the semiconductor substrate 101. The first oxide layer 104, the silicon nitride layer 103, the pad oxide layer 102 and the semiconductor substrate 101 are partially removed to form at least one trench structure 105 on the semiconductor substrate 101 by conventional photolithography and etching processes. Thereafter, as shown in FIG. 1(b), the second oxide layer 106 is formed on the bottom and the sidewalls of the trench 105 and on the surface of the first oxide layer 104 by High Density Plasma Chemical Vapor Deposition (HDPCVD) process.
After an etching process is performed to remove the second oxide layer 106 on the sidewalls 1051 of the trench 105, as shown in FIG. 1(c), only a small portion of the second oxide layer 106 on the bottom of the trench 105 will remain and be defined as a bottom oxide layer 108. Afterwards, as shown in FIG. 1(d), a conductive layer 107 is allowed to fill in the trench structure and deposits on the second oxide layer 106, and the conductive layer 107 usually comprises polysilicon.
Because in the conventional process, the second oxide layer 106 is formed with High Density Plasma Chemical Vapor Deposition (HDPCVD) process, the second oxide layer 106 will be formed with a ladder shape. The conductive material 107 will be deposited along the ladder-shaped second oxide layer 106 in the HDPCVD process. As a result, a void 1052 is formed in the conductive material 107 on the trench 105 as shown in FIG. 1(d). Because of the existence of the void 1052 in the conductive material 107 on the trench 105, after a planarization process is subsequently performed, as shown in FIG. 1(e), portions of the void 1052 would be exposed, and a cavity 10521 will be formed in the conductive material 107 on the trench. Thus, the effect of the point discharge would occur on the cavity 10521, and the current leakage will also easily occur when semiconductor devices are used.
Therefore, it is desirable to develop a method of forming a bottom oxide layer and conductive layers in the trench without the formation of voids while the trench is filled with the conductive layer, and a method of preventing the current leakage of semiconductor devices.